Electron discharge device



Aug. 19, 1947. B. LLEWELLYN 2,425,743

ELECTRON DISCHARGE DEVICE Filed March 11, 1941 3 Sheets-Sheet 1 "Illmum/r T I A iii. ILF. ourrur [Ni [Um F. a. LLEWELLV/V .arroklvtr 1947.F. B. LLEWELLYN 2,425,748

ELECTRON DISCHARGE PEVICE Filed March 11, 194]. 3 Sheets-Sheet 2 in Irrnvs warn c5 7 M Jam/agar '1 wfi INVENTOR E B. LLEWELL YN ATTORNEY Aug.19', 1947.

MI. INPUT Filed March 11, 1941 3 Sheets-Sheet 3 FIG. 7

I Mr. ourrur I0! I02 I04 I I I FIG. 8

INVENTOR EB. LLEWELLVN ATTORNEY Patented Aug. 19, 1947 UNITED STATESPATENT OFFICE Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York Application March 11, 1941,Serial No. 382,683

24 Claims. (Cl. 179-171) This invention relates to high frequencyelectronic devices for the production, amplification, or conversion ofultra-high frequency waves and particularly such devices as arecharacterized by critical electron transit times.

A principal object of this invention is to secure eflicientamplification of ultra-high frequency waves. in the order of at least3,000 megacycles, using moderately low voltage electron tubes.

An additional object of the inventionis to produce or controloscillations of the order of 3,000 megacycles and higher in frequencywith simpler discharge structures than those which are now effectlve forthose purposes.

An additional object of the invention is to increase the availabletransadmittance of space charge controlled discharge devices atfrequencies of the order of 3,000 megacycles and higher.

An additional object is to avoid the requirements for relatively highvoltages, electron focussing and other complexities characteristic ofavailable expedients such as devices employing velocity variation" orvelocity modulation as it is sometimes called.

A further object is to make available a device inherently capable ofproducing a'degree of amplification at wave-lengths of the order of afew centimeters comparable to that heretofore attain. able only at wavelengths of the order of a few meters.

Another object is to provide in such a device strictly unilateralamplification, that is, amplification where the transfer of highfrequency energy shall be in only one direction, from input to output.

Efforts to operate space charge control tubes at frequencies of theorder of 3,000 megacycles using the moderate electrod potentials, e. g.,200 to 400 volts, customary in lower frequency systems have met withlittle success. Some of the factors causing difllculty havebeenappreciated; for instance, the input loading at high frequenciesoccasioned by an effective shunting resistance between cathode and gridhas been discussed at some length in various publications such as thearticles "Operation of ultra-high frequency vacuum tubes. by F. B.Llewellyn, Bell System Technical Journal, October 1935, pages 632 to665; "Analysis of the effects of space charge on grid impedance. by D.0. North, Proceedings of the Institute of Radio Engineers, January 1936,pages 108 to 136; and The operation of electron tubes at highfrequencies by H. Rothe, Proceedings of th Institute of Radio Engineers,July 1940, pages 325 to 331. The various theoretical studies togetherwith the results of experimental work have led to the general conclusionthat, above certain operating frequencies, barriers exist which precludethe useful operation of space charge control tubes. As a result it hasbeen widely supposed that the transadmittance of tubes of the ordinarytypes decreases in magnitude as the frequency is increased thusinterposing a definite barrier at frequencies even below 3,000megacycles. v

Recourse has been had to the velocity variation type of device in whichthe primary electron control is exercised through variation initially ofelectron velocities rather than of the density of the electron stream.Some success has been had with devices of this type but in general theycall for the use of electrode voltages oi. the order of 500 to 1,000volts or higher and accurate focussing of the electron stream and thetransadmittance attained is not particularly high.

The applicant has discovered that in devices operating according to thegeneral principles of the ordinary space charge control types of tubesto which reference has been made, the transadmittance actually does notdecrease in magnitude as the frequency is increased if the tube issuitably designed and operated. The problem then becomes one of makinguse of that transadmittance properly. This problem has been solved inaccordance with this invention by determining the conditions ofoperation under which the space charge control type of tube is notsubject to the limitations with respect to operating frequency whichheretofore have always been encountered and which, because of lack ofknowledge of the means of avoiding them have hitherto been thoughtunavoidable.

Previous efiorts to make a conventional tube such as a pentode amplifyat frequencies of the order of 3,000 megacycles have uniformly failed.This was principally because such structures exhibited an inherent lossin the input circuit com. prising the cathode and control grid, referredto above as input loading, of such a magnitude as to nullify the effectof the transadmittance and to conceal the fact of its existence. Thsolution of the problem begins with an appreciation that the magnitudeof the transadmittance inherent in the electron stream may be maintainedat high frequencies and that the problem is really that of making theamplifying eilect of the transadmittance usefully available. A step inthat direction is the further appreciation that if the oath. ode to gridzone of an electron discharge device be electrically isolated from theremainder of the device, except, of course, to permit passage of theelectron stream, it may be dealt with as a diode. It is possible toreduce the net resistance of a diode to any desired degree or even tomake it negative by suitable design which will establish the electrontransit time within the regions of 1 to 1 cycles or 2 to 2% cycles,etc., as is explained in detail in U. S. Patent 2,190,668, February 20,1940. With the grid-cathode diode properly isolated and with its transittime such as to effectively annul the grid circuit loss a majorbeclouding effect is removed and the inherent transadmittance of theelectron discharge device is made available. The grid may at one and thesame time serve to electrically isolate the grid-cathode zone from theremainder of the device and to effectively couple the input circuit tothe electron stream. Inasmuch as the transit time requirements permit arelatively wide spacing of the cathode and control grid and also permitmoderate space current voltages to be used the solution of the tubedesign problem is greatly facilitated.

Since energy transfer by an electron discharge amplifier requires acoupling between the input circuit and the electron stream and a secondcoupling between the electron stream and the output circuit it isdesirable to make the couplings to the electron stream as intimate andeffective as possible. In the case of the output cir cuit a verydesirable expedient is to employ a low loss closed electrically resonantshell into which the electron stream may be introduced or through whichit may pass. If the stream enters the out put resonator shell through afine grid and, if passing through the shell, leaves through a similargrid, the output resonator serves to improve the electrical isolation ofthe input diode. The gap or transit path between the grids, or betweengrid and anode, of the output resonator should be short in order tomaintain the transadmittance at a high magnitude at high frequencies.The mag.

nitude of the transadmittance is substantially the same as would beproduced in a low frequency tube of the same dimensions and operatingvoltages when the transit angle across the output gap is small. Thetransit time should be less than a cycle of the high frequencyoscillation and preferably small with relation to a cycle.

In accordance with the principles of the invention which have beenoutlined, an electron v discharge amplifier for very high frequencieswill comprise a structure quite different from that of the usual lowfrequency amplifier with its container of glass or similar dielectricmaterial through which pass wire leads for providing electricalconnection between the circuit and the tube electrodes. Instead, in apreferred form, two substantially closed resonant conducting shells areprovided, one of which constitutes the input circult and the other theoutput circuit. Within .the input circuit is a cathode spaced at acritical electrical distance, for example, 1% cycles transit time from agrid through which the electron stream leav s the input shell. Theoutput shell is provided with closely spaced grids, or closely spacedgrid and anode, which mark the end points of the transit of the streamthrough the shell. In practical application the transit angle throughthe output shell may be given values from the minimum readily attainableup to many hundreds of degrees but preferably less than 90 degrees atwhich the magnitude of th transadmittance will have decreased only about10 per cent below its maximum magnitude which occurs at very smalltransit angles. With such a, structure a transadmittance of severalthousand micromhos has been obtained at a frequency of 3,000 megacyclesas compared with a transadmittance of a few hundred micromhos with avelocity variation type of tube.

The invention will be understood more fully from the following detaileddescription and the illustrative embodiments shown in the accompanyingdrawings.

In the drawings:

Fig. 1 shows in one form a space charge control amplifier embodying theprinciples of the invention;

Fig. 2 shows an amplifier arrangement operating according to certainprinciples of the invention;

Fig. 3 shows an alternative form of amplifier embodying the invention,Differences from the arrangement of Fig. l are that the electroncollector is separated from the high frequency electrodes and the inputand output resonant systems are physically separate;

Fig. 4 shows a tube similar in operation to that of Fig. 1 but in whichthe elements are cylindrical and the electron emission is radial;

Fig. 5 shows a tube embodying the invention in which both the cathodeand the anode are separate from the high frequency electrodes and anadditional electrode is shown as an electron accelerator for the p p seof producing a virtual cathode near the high frequency input electrodes;

Fig. 6 shows a three-stage amplifier embodying the invention andincluding a feedback circuit which may be used to improve thetransmission characteristic; Fig. 7 shows an embodiment of the inventionwherein the electron tube utilizes only three elements, a cathode, ananode, and a single control grid of special form intended to serveeffectively as a shield between theinput and output circuits; and

Fig. 8 shows a modification of a portion of Fig. 1 adapting it to use asa high frequency converter.

Fig. 1 shows a cylindrical conducting shell 8 which forms portions ofthe amplifier input and output circuits and, being evacuated through tu-50 bulation 21, serves also as the envelope of the electron tube. Thecathode, control grid, screen and anode are shown at 5, 9, II and 6,respectively. The sources of biasing potentials, l6, l1 and I8, may besuch that the first or control grid 55 is negative with respect to thecathode while the screen and anode are positive with the anode at asomewhat higher potential than the screen.

Maintenance of the control grid negative with respect to the cathode isnot important for critical transit time operation as it is for the usuallow frequency type of operation so that here the potential may be eitherpositive or negative with respect to the cathode. The cathode isindirectly heated by means of the heater l9 which 5 is energized frombattery l5. Thecathode temperature is preferably adjusted to secureemission only slightly in excess of that required to provide completespace charge in the electron stream. It will be noted that the cathodeheater 70 is entirely enclosed within th cathode sleeve. It

is important to provide means for thermal attenuation in order to directas much of the heat as possible to the coated surface 5 and thus avoidthe introduction of the losses which occur when 70 the high frequencyconducting surfaces are operated at very high temperatures. In thefigure,

a simple means of heat attenuation is provided by forming the walls ofthe cathode sleeve with an extremely thin portion at 26 Just behind theactive surface thus retarding the flow of heat in the direction awayfrom the coated surface 5.

For the high frequency, the input circuit is formed by the cavityresonator I, where the outer shell 8 comprises the external conductor,the cathode together with its sleeve 2I-forms a reentrant member and thecontrol grid 8 mounted in the center of an annular member ill closes theend efl'ecti eiv, l wing electrons to pass through but confining nearlyall of the input energy to the cavity l. The grid 9, and also screen II, may be of parallel wires, a wire screen, or other form ofconstruction which provides good electrical shielding while permittingthe passage of electrons. Similarly, the output circuit is a cavityresonator, 2, whose outer conductor is formed by the shell 8, while theanode 6 together with its support comprises a reentrant member and thescreen ii mounted in the center of the annular member I2 closes the endeffectively, allowing the electrons to enter, but confining nearly allof the output energy to the output cavity 2. It will be noted thatinsulation for the polarizing potentials is provided by the insulatingsleeves I 3 interposed between members and flanges of sufllcient area toprovide capacitances of negligible impedance to the high frequency. Theglass, or equivalent, seals at points 1 and points i4 provide vacuumtight means for the introduc-'- tion of electrical connections throughthe envelope of the electron tubeto members within.

The space between the control grid 9 and the screen Ii is relativelyfield-free and provides additional means of segregating the outputcavity from the input cavity and thus eliminating mutual couplings. Thetwo grids, 9 and I I, might be replaced by a single one providingsufficient segregation of thetwo cavities is obtained, or, on the otherhand, additional grids might be interposed between those shown in thefigure for the I purpose of improving the screening, removing unwantedsecondary electrons or for other purposes in the well-known manneremployed at low frequencies. An example of single grid construction isshown in Fig. 7.

In operation the input signal to be amplified is introduced into thecavity i and the amplified output energy is extracted from the cavity 2.Many methods are available for accomplishing these results. The methodshown in Fig. 1 utilizing coupling coils and 2! which may be connectedby the terminals shown to a suitable high frequency input source and toa high frequency load, respectively, is merely illustrative. Anothermethod of coupling is illustrated in the feedback connection, providedby coaxial line 22, 23, where portions of conductor 23 simply project ashort distance into the cavities and thus couple with the high frequencyfields within.

The feedback connection shown in Fig. 1 utilizing the coaxial linecomposed of outer conductor 22 and inner conductor 23 is not essentialto operation of the device as an amplifier. It is shown to illustrate ameans of transferring energy from the output portion of the device tothe input portion in a controlled manner to provide either regenerativeoperation, self-oscillation or inverse feedback to improve stability andreduce distortion. mined by the adjustment of the couplings and thephase may be determined, tomake the feedback The amount of feedback isdeter regenerative or inverse in character, by Just-'- ment of thelength of the connecting line.

The operation of the arrangement of-Fig. 1 may be outlined as follows:Under the influence of the biasing potentials between the cathode andthe other electrodes a stream of electrons passes from the cathode I,through the control grid 8 and the screen Ii to the anode B. Theelectron stream thus passes through the gap 3 in the input cavityresonator and the gap 4 in the output cavity resonator. In each of thesegaps there is a high frequency electric field when the input resonatoris excited by a high frequency input and high frequency is generated inthe output resonator, these resonators being constituted as previouslydescribed. The electrons flowing across gap 3 are grouped by spacecharge variation caused by the high frequency input which varies at highfrequency the potential between the control grid 9 and the cathode 5.Thus an electron stream, the density of which varies in accordance withthe input signal, passes out of gap 3 and through the space between thegaps 3 and 4. This space is relatively free of high frequency field andthe degree of space charge within it may be controlled by the biasingpotential on the ad- Joining electrodes. The density variations in theelectron stream (sometimes called bunches) progress across the spacewithout substantial decrease in amplitude, are impressed across theoutput circuit at gap 4 thereby inducing the desired output in resonator2 and are collected on anode 8. It should be noted here that theelectrons enter the space between gaps 3 and 4 having been alreadygrouped into bunches so that this space, free of the high frequencyfields, through which the electrons drift, unlike the drift space indevices utilizing the so-called velocity modulation principle, is notcalled upon to perform the grouping function. This grouping function andother characteristics of velocity modulated tubes have been described inan article "Velocity modulated tubes, by W. C. Hahn and G. F. Metcalf inthe Proceedings of The Institute of Radio Engineers, February 1939,pages 106 to 116, concerning a tube somewhat similar in appearance toFig. 1 but different in principle and method of operation.

Another type of amplifier which superficially resembles the arrangementshown in Fig. l is the so-called inductive output type such as isdescribed in the article "An ultra-high frequency power amplifier ofnovel design, by AndrewV. Haefl' in Electronics magazine, February 1939,pages 30 to 32. In that amplifier the electron discharge is controlledby a space charge control grid and the output energy is generated in aresonant cavity much as is done in the arrangement of Fig. 1. However,there are important 'difierences between the amplifier described byHaefl and the arrangement of Fig. 1. Very complete shielding of theelectrical circuits and the electron stream is a feature of Fig. 1, and,while the Haeif amplifier utilizes high velocity electrons to minimizetransit time effects in the input circuit and also between the input andoutput circuits, the arrangement of Fig. 1, like the arrangement of theother figures following, utilizes a transit time across the input spacecritically related to the operating high frequency to minimize the inputloading effects and does not require a small, or even a critical,transit time in the space between input and output. This is obviouslyadvantageous since it allows latitude in the spacing of the inputelectrodes and permits the use of 7 moderate electrode biasing voltagesrather than excessively high voltages such as are required to acceleratehigh velocity electrons.

In one aspect the arrangement of Fig. 1 might be looked upon as a typeof "grounded grid" amplifier. Such amplifiers have been used to someextent at low and moderately high frequencies and are found to have thedisadvantage that the output current flows through the input energy pathproducing a type of feedback which does not cause oscillation butproduces a low impedance at the input. The system of Fig. 1 does notoperate in this fashion because with the exception of any couplingthrough the feedback connection through line 22, 23 which iscontrollable advantageously as has already been indicated, the input andoutput systems are completely shielded from one another so that no highfrequency from the output can get back to the input circuit. The leakagethrough grids 9 and II is not suflicient to affect this conditionappreciably and for even better shielding than shown in Fig. 1 anadditional grid may be interposed between 9 and II or the distancebetween 9 and II may be lengthened. High frequency in the direct currentsupply leads is obviated by the shielding and adequate by-passcapacitances where the direct current leads are connected to theenclosed high frequency systems. Thus the bunched, or variable currentflowing inside the tube is entirely smoothed out for external leads bythe flow of displacement current.

It has been mentioned that a feature of the invention is the reductionof input loading by operating with the input electron transit timecritically related to the operating frequency. It has been shown inapplicant's Patent 2,190,668, dated February 20, 1940, which will bereferred to later, that when the duration of electron transit timebetween two electrodes, such as across gap 3 between cathode 5 andcontrol grid 9, lies between 1 and 1 or between 2 and 2 /2, etc., cyclesof the operating high frequency, the loading resistance produced by theelectron stream is negative in sign. When the electron current is notsuillciently large to cause this negative resistance to exceed thepositive resistance of the resonant input system and connected circuits,no singing oscillations can occur and the negative input loadingresistance can, therefore, be used to compensate for the extra losses inthe input system caused by the presence of the hot cathode surface 5.

The production of negative loading resistance, rather than positive, byoperating with critically related electron transit time across the inputelectrodes in this amplifier arrangement is similar to the production ofnegative resistance in diodes as described in the before-mentionedapplicant's Patent 2,190,668, dated February 20, 1940. Reference may bemade to that patent wherein an equation is developed relating theresistance of an electron stream and the electron transit time and acurve of the equation is plotted (Fig, 3 of said Patent 2,190,668)showing the regions where the resistance is negative. This figure showsthat, as previously stated, the resistance is negative when the transittime is between the periods of 1 and 1 /2 or between 2 and 2 /2 orbetween 3 and 3 /2, etc., cycles of the operating high frequency.

The greatest negative values of resistance occur when the transit timeis substantially the period of 1 A, 2%, 3%, etc., cycles of theoperating high frequency.

In applicant's copending application, Serial No.

319,414, filed February 17, 1940, now Patent No. 2,308,523, datedJanuary 19, 1943, is described the use of a diode operated in thismanner to compensate for high frequency circuit resistance.

The principle, the production of negative resistance by criticaladjustment of input electron transit time, is utilized in this inventionto compensate for and thus effectively eliminate input loading in highfrequency amplifiers and the like. In Fig. 1, for example, the inputelectron transit time is the time required for an electron to traversethe gap 3 between the cathode 5 and the control grid 9 and its durationis determined by the spacing of the tube electrodes and the polarizingvoltages employed. The usual, though not essential procedure to obtainthe proper input transit time is to fix appropriately the anodepotential by source l8, the screen potential by source I! and make thefinal adjustment that of the control grid potential by source I6. Theanode 6 must, of course, be positive with respect to the cathode.

, The screen II and control grid 9 may be either positive or negativewith respect to the cathode.

As has been previously mentioned, the length of gap 4, between the gridII and the anode 6, and the biasing potentials are so related that theoutput electron transit time, across gap 4, is made short, preferablyless than a cycle of the high frequency, to maintain the transadmittanceat a high magnitude.

It is noteworthy that when the input electron transit time is the periodof several cycles, rather than only 1 or 2, the tendency for theelectron stream to produce input loading gradually decreases withfurther increase in the number of cycles required as is indicated by thedecreasing amplitude of the curve of Fig. 3, Patent 2,190,668,previously referred to. Thus at the extremely high frequencies electronsmay be allowed to consume a good many cycles in their transit across theinput space, and the adjustment called for by the requirement of a wholenumber of cycles plus a quarter for the transit time becomes lesscritical as the number of cycles becomes larger. It is true that therewill then be less negative resistance available to compensate forcircuit losses, but on the other hand, neither will there be severeloading in case the adjustment for producing the desired transit timeshould change for any reason. It follows that the tolerances to whichthe biasing potentials must be held for the purpose of maintainingproper electron transit time do not become impractically severe at thehigher frequencies where the input transit time may be made to extendover several cycles as for convenience in construction.

Proper electron transit time adjustment must be supplemented by suitablephysical structures in order to achieve substantial high frequencyamplification, and space charge control tubes constructed as in the pastfor low frequency applications are not at .all well adapted to use inamplifiers for 10 or 20 centimeter waves. Thus, important features ofthis invention are the physical embodiments which conform to theconditions under which amplification is possible at these highfrequencies, and under tube operating conditions comparable to thoseusual in operation at lower frequencies. The possibilities attainableare indicated by the results of tests on preliminary designs of tubesand circuits based on the invention. In one such test an amplifieremploying the principles described above and illustrated by Fig. 1, butwithout a feedback arrangement such as line .22, 23 and with inherentregeneration reduced to an inappreciable amount by care in the reductionof stray coupling between input and output, gave a gain of 9.5 decibelsat a wave-length of 18 centimeters whenthe total cathode emission wasonly 18 mllliamperes and when the highest potential employed was notmore than 400 volts on the anode. In the particular tube used, thecathode-grid separation was about 0.015 inch. The grid-screen separationwas 0.125 inch and the screen-anode separation was 0.015 inch. Thecathode diameter was inch and the whole of its flat end-surface wascoated with thermionic emitting material. The grid was operated at apositive potential to secure the desired emission with an input electrontransit time (between the cathode and the grid) the period of about 1%cycles of the operating high frequency. In order to reduce the effect ofsecondary emission from the screen, its bias was made approximately thesame as that of the grid. It may be noted that on account of the variouselectrode biasing potentials the electron velocity may be different overdifferent portions of the electron path so that the relative electrontransit times through the input and output gaps are not necessarilyproportional to the relative physical lengths of those gaps. Thus in theinput gap the electrons may be traveling relatively slowly while in theoutput gap the potentials are such that their velocity is much greaterand in practice the lengths of the gaps may be equal.

Fig. 2 shows a tube and circuit arrangement which was one of the firstto be tested according to the principles of the invention. The structureis not ideal and embraces compromises which are avoided in preferredarrangements illustrated in other figures. Designation numbers which arethe same as on Fig. 1 indicate similar elements in the two figures, InFig. 2 the vacuum tube elements are enclosed in an evacuated envelope 40and the output resonant cavity 2 enclosed by the conducting shell 42 isattached to two rings 43 and M sealed into the envelope. The openings inthe rings 43 and 44 within the tube are closed with mesh grids ii and 30thereby enclosing between them a portion of the output cavity 2 and thegap 4 corresponding to the output gap 4 in Fig. 1. The flanges 3'! and38 were added as shown simply to add capacitative loading to decreasethe resonant frequency of the output system to correspond to what couldbe introduced into the input of the tube. This expedient was necessaryonly because of the somewhat unsatisfactory structure of the inputportion of this particular tube.- The supporting structures and leadsfor the cathode and the adjacent control grid were of such nature thatthey acted as a filter for frequencies above 430 megacycles. The inputfrequency employed was, therefore, selected as 384 megacycles which wassupplied through the input system shown, requiring, however, loading theoutput system with the flanges 3i and 38. The anode 6 is independent ofthe high frequency electrodes II and 30 and resistor 36 is inserted inthe lead to 6 to prevent spurious oscillations. The input system I is ofthe coaxial type comprising the outer conductor 4i and inner conductor39. The high frequency input voltage is applied to these conductorsthrough the input line 3|, 32. The high frequency voltage betweenconductors 39 and 4| is applied between the cathode 5 and the spacecharge control grid 3 by leads 45 and 43, respectively. The tubeoperates as explained in connection with Fig. 1. Space charge control ofthe electron stream is exerted by the high frequency input voltageacross the input gap 3 between cathode 5 and control grid 3. The groupedelectrons then proceed to grid ii and cross the output gap 4 between thegrids Ii and delivering energy to the output resonant system 2. Highfrequency output is taken oil through the coaxial line 34, which iscoupled to the high frequency field in the space 2 as shown. Aspreviously explained, the electron transit time across the input gap 3is adjusted to minimize the input loading and the electron transit timeacross the output gap 4 is made short to maintain the gain at highfrequencies. While this tube, the most appropriate available at thetime, did not have the best type of input connections for high frequencyoperation it produced amplification at 384 megacycles (wave-lengthapproximately 78 centimeters) consistent with its trans-conductancemeasured at low frequencies. Such performance, together with the resultsof later tests at shorter wave-lengths with more suitable tubestructures as referred to previously, under operating conditionsaccording to the teachings of this invention show the soundness of theprinciples involved and indicate that, within the limitations ofphysical structure, amplifier performance essentially equivalent to thatat low frequencies may be had at very high frequencies.

During the course of the experiments with the arrangement of Fig. 2, itwas found that by adjusting the input to sufllcient amplitude and tuningthe output resonant system to the harmonic frequency three times that ofthe input by removing the capacitance loading of flanges 37 and 38, anoutput at the higher frequency was obtained. Thus with an input at 240megacycles, output power at 720 megacycles was obtained.

Fig. 3 shows an arrangement differing from Fig. 1 in that an evacuatedglass envelope is employed, no feedback is shown, and the anode isseparate from the high frequency output electrodes. In another aspectFig. 3 may be considered similar to Fig. 2 except that a more suitableinput system is substituted for that of Fig. 2. In this figure, as inthe others, designation numbers carried over from earlier figuresindicate elements similar to those bearing the same numbers in theearlier figures. The input resonant cavity I is enclosed by cathode 5,conducting members 25, 4| and 50, and control grid 9. The outputresonant cavity 2 is enclosed by screen i I, conducting members 43, 42and 44, and screen 30. Members 50, 43 and 44 are rings sealed into theglass envelope. The openings in these rings within the envelope arecovered with the mesh screens 9, ii and 30 which allow the passage ofelectrons from cathode 5 to anode 6 but are substantial barriers to theescape of the high frequency electric fields within the resonantcavities. Thus the input and output electric fields are well shieldedfrom each other and from the electron stream except where it passesthrough the input field in the gap 3 between the cathode 5 and thecontrol grid 9 and where it passes through the output field in the gap 4between the screens II and 30. A high frequency input is connected tothe terminals of the coupling coil '28 for excitation of the inputresonant system and .the high frequency load is connected to theterminals of coupling coil 2! for extraction of energy from the outputresonant system. The input and output circuits may be connected togetherfor feedback or regeneration as illustrated in Fig. 5. The operation ofthis circuit is the same as ex- 11 plained in connection with Fig. l,the electron stream being space charge controlled in gap 3 anddeliveringenergy to the output circuit in gap 4, the electron transit times beingadjusted as previously described.

Two useful features of Fig. 3 resultfrom the separate position of theanode 9. First, the anode may be operated at a lower potential than thescreens II and 30 and hence the small output transit time may bemaintained at the same time that the power efficiency of the system isincreased. Second, by adjustment of biasing potentials secondaryelectrons from the plate may be timed to return through the output gap 4between screens II and 39 in the proper phase to add to the outputenergy. In such operation the anode should be coated with a goodsecondary emitting surface as indicated at 5 I.

Fig. 4 illustrates a modification employing a cylindrical form ofstructure. Various components in the drawing are numbered to correspondwith similar components of previous Figs. 1, 2 and 3. The evacuatedenclosure for the tube elements comprises conducting shells 99, 91, 98and 6-9, and the seals of glass or other insulating material designatedI. The cathode 5 emits electrons radially in all directions through thespace charge control grid 9 and the screen II to the anode which is theconducting member 69. In this instance, therefore, the electron pathextends in all radial directions from the cylindrical cathode and theintercepting members 9, II and 69 are in the shape of curved surfaces ofcylinders. The input resonant cavity I i enclosed by the cathode 5,members 66, I9, 60, II and 61, and the control grid 3. It will be notedthat this is a coaxial system closed at one end by the flanges 62 and 63and at the other end by the member 60. The annular space between 69 andII and the insulating disc between flanges 62 and 63, designated I3,provide insulation for biasing potentials and are of suflicient area toprovide low impedance by-pass capacitances for the high frequency. Theoutput resonant cavity is enclosed by the screen 4, and members 58, 69,I3, GI and I2. This also is a coaxial system closed at one end byflanges 64 and 65 and at the other end by member 6|. The insulating discbetween two flanges 64 and 65, designated I3, and the annular spacebetween members 13 and SI eparate the biasing voltages and provide lowimpedance bypass capacitances :fOr the high frequency. The inputresonant system is shown energized through the coaxial line 3|, 32, froma high frequency source 33 and a high frequency load is represented at14 coupled to the output resonant system through the coaxial line 34,35. This tube and circuit, illustrated in Fig, 4, operate a has alreadybeen described in connection with Fig. 1. The electron stream is spacecharge controlled and the electrons are grouped immediately in the inputgap 3, between the cathode 5 and control grid 9. The grouped electronsthen pass through the gap 4, between the screen I I and the adjacentportion of member 69 which serves as the anode, delivering highfrequency energy to the output system in accordance with the highfrequency input from 33. The electron transit times across the gaps 3and 4 are adjusted for optimum performance as previously described. Thecylindrical structure has the inherentgdisadvantage that the outputcircuit consists of a coaxial line whose geometrical relations are suchthat it i diflicult to make the ratio of inner and outer conductorslarge enough to secure as high output impedances as may be procured withother structures such as that of Fig. 1. However, in broad bandapplications where extremely high output impedance is not desirable thestructure of Fig. 4 may be advantageous.

Fig. 5 illustrates another modification in which the cathode is removedentirely from the high frequency field and a space charge grid iinterposed between it and the input gaps to accelerate the electronsand, if desired, to form a virtual cathode very close to the input gap.The output resonant system is the same as that of Fig. 3. The inputresonant system differs from that of Fig. 3 in that the conductingenclosure does not include the cathode and its supporting member 25 butincludes instead a ring 83 and screen 82 such that the input gap 3 isbetween the screen 82 and the space charge control grid 9 rather thanbetween the cathode 5 and the control grid 9 as in Fig. 3. The gridmounted in the sealed-in ring M is operated at a positive potential withrespect to the cathode to draw electrons from the cathode while thescreen 82 is maintained at a potential very nearly the same as that ofthe cathode. Potential adjustments may be such that the grid 80 servessimply to assist in the drawing of electrons from the cathode or suchthat a virtual cathode is formed very close to the screen 82. In eithercase the flow of electrons through the input gap 3 between screen 82 andgrid 9 is governed by the space charge control of grid 9 due to the highfrequency input voltage between it and screen 82. The electrons areimmediately grouped in the gap 3 and thereafter deliver energy to theoutput system in passing through the output gap 4 between screens I Iand 30, finally being collected at the anode 6. Operation is thus thesame as that of the previously described figures. As mentioned inconnection with Fig. 3, the anode may be provided with a secondaryelectron emitting surface 5| and potential adjustments made so that thesecondary electrons pass through the gap 4 at the proper time tocontribute to the output. The input-output connection through coaxialline 22, 23 is not essential to operation but may be used to provideregeneration or feedback as explained in connection with Fig. 1. Theinsulating disc l3 between the flanges 85 and 86 separates the biasingvoltages on the conducting shells 4| and 42 of the input and outputresonant systems. The high frequency path through the outer conductor 22of the feedback line is maintained through the capacitance between theflanges 85 and 86.

Fig. 6 illustrates a three-stage amplifier in which each stage issimilar to the arrangement of Fig. 1 with the exception that glassenvelopes enclose the vacuum tube elements. The elements of the threetubes which are connected in cascade are enclosed in the envelopes 90,9| and 92. The elements in the three tubes are similar and are similarlydesignated, as in Fig. 1. It will be observed that the type of structureillustrated is practically identical with that of Fig. l. Thecylindrical conducting shell 8 which bounds all of the resonant cavitiesdoes not, however, serve as the evacuated envelope in Fig. 6 as it doesin Fig. 1. The resonant systems are separated from each other by theflanged rings 95, 96, 91, 98, 99 and I00 in which are mounted thecontrol grids 9 and the screens II. These rings are shown sealed intothe glass envelopes. An alter-native and possibly preferableconstruction is to attach them externally to the envelopes to otherrings which are sealed into the envelopes, such as ring 13 II in Fig. 3.The insulating sleeves II, as in theearlier figures, function toinsulate the polarizing voltages but by virtue of the capacitancesbetween the conductors which they separate they provide low impedancepaths for high frequency currents.

The input resonant system I of the amplifier and the first tube isenergized from a high frequency source connected to the input coaxialline 3|, 32. The output resonant system 2 of the amplifier and the lasttube is coupled to an output coaxial line 34, 35 which is connected to ahigh frequency load. Each of the intermediate resonant systems 93 and 94serves as the output circult of the preceding tube and the input circuitof the following tube. Each intermediate cavity 93 and 94 iselectrically and physically longer than the terminal resonant systems Iand 2 so that a node in the'standing wave of the high frequency fieldexists midway between the bounding rings, 96 and 91, and 98 and 99. Thuseach system, 93 and 94, functions somewhat as if separated into twoparts by a conducting plane passed through the center perpendicular tothe axis but with the two parts coupled together electrically. The leadsfor energizing the cathode heaters and for biasing the anodes arecarried through the space in the resonant systems 93 and 04 in thepositions of the nodes in the high frequency fields to minimize thecoupling between these leads and the fields. As an added precautlon itmay be found desirable to shield these leads and provide high frequencyby-pass capacitances where the leads leave the shell 8. The coaxial line22, 23 shown coupling the input and output resonant systems may be usedif desired to provide either regeneration or negative feedback. Asmentioned in connection with Fig. 1, the amount of regeneration orfeedback may be varied by changing the degree of coupling between theline and the resonant systems and the phase may be varied by changingthe length of line between the two systems.

It is the usual practice to make the input and output resonant systemsof the amplifiers such as have been described resonant at the samefrequency, that of the input which is to be ampli fled. However, forcertain purposes it may be desirable to tune them to differentfrequencies. For instance, as was indicated in connection with Fig. 2,the output system may be tuned to a harmonic of the input frequency toobtain an output at a frequency harmonically related to that of theinput. Also, where a band of frequencies is to be amplified the inputand output systems may be tuned to somewhat different fre quencies toequalize transmission over the band and particularly the resonantsystems in a multistage amplifier such as that of Fig. 6 may be maderesonant at such neighboring frequencies as are desirable to transmit aband of frequencies. Such frequency bands would not ordinarily be sowide as to interfere with satisfactory adjustment of the electrontransit times.

Fig. 7 illustrates a single-stage amplifier arrangement similar inelectrical arrangement to Fig. 1 or each stage of Fig. 6 in that thecathode and anode of the electron tube form portions of the boundariesof the input and output resonant cavities. Here, however, a single gridelectrode I103 is interposed between the cathode and anode rather thantwo, as 9 and II shown in Figs. 1 and 6. This single grid is ofconducting material, relatively thick, with small holes through it inthe direction of the electron flow to permit free passage of electronsfrom cathode to anode through the gaps 3 and 4 in the input and outputcavities. The relatively long, small diameter holes through the thickgrid electrode, while permitting the passage of electr effectivelyprevent the transmiwion of high frequency energy and consequentintermingling of the high frequency fields on either side of the grid inthe input and output cavities. An alternative method of constructing thegrid electrode, not shown. is to use what is in effect a thick memberwith narrow slits rather than holes so that the structure consists of aseries of slats much like those of a window shutter with the slats inthe open, or horizontal, position. With such an electrode the relativelylong passage between the slats from one side of the electrode to theother isolates the input and output high frequency fields.

The cathode 5, control grid I03 and anode 4 are supported by the ringmembers IOI, I02 and I04, respectively, which are sealed into the glassenvelope 40. The input resonant cavity I, which is energized from thehigh frequency source 33 through the coaxial line 3|, 32 is bounded bythe coaxial cylindrical members I05 and I01, the separating member I00,grid electrode supporting member I02, grid electrode I03, cathode 5,cathode supporting member IN, and closure members I09 and H0. The outputresonant cavity 2, from which the amplified high frequency energy istransferred to load I4 by coaxial line 34, 35, is bounded by the coaxialcylindrical members I06 and I01, the separating member I08, gridelectrode supporting member I02, grid elecr trode I03, anode 6, anodesupporting member I04,

and closure members III and H2. The closure members E09, IIO, III and H2are annular conducting rings which are movable axially to adjust thesizes of the resonant cavities. Rings I09 and III fit closely tocylindrical member I01 while rings H0 and H2 fit closely to cylindricalmembers I05 and I06, respectively. The gaps between rings I09 and H0 andbetween rings III and II2 are short and the ring surface areas facingeach other across the gaps are of sufficient area to provide a lowimpedance capacitative path for high frequencies and to effectivelyclose, to high frequency fields, the cavities I and 2 while serving toisolate the'biasing voltages connected to the tube electrodes.

The operation of the Fig. 7 device is the same as that of Fig. 1considering that the single grid electrode I03 takes the place of thetwo grids 9 and ii shown in Fig. 1. A feedback connection may be addedto the Fig. 7 showing to provide regenerative or oscillatory action suchas the coaxial line 22, 23 of Fig. 1 or any other suitable means.

Fig. 7 illustrates more strikingly, perhaps, than the other figures areason why, as previously mentioned, the necessity for focussing theelectron stream may be avoided in this type of tube. The reason is thatthe electron path is not long. For instance, in one particular tubeconstructed, the distance from the cathode to the anode is inch with acathode diameter of inch. Therefore, it can be seen that an acceleratingvoltage Will produce practically linear electron iiow whereas withalternative high frequency amplifier tubes the distance from cathode toanode is comparable or large compared with the diameter of the electronstream requiring external means to keep the electron flow parallel.

It has been stated that a device according to this invention isadaptable to the conversion of high'frequency waves. One suchapplication is where two different frequencies are applied to the inputof a device and a frequency equal either to the sum or difference of thetwo input frequencies is derived from the output as in the production ofthe intermediate frequency in a heterodyne radio receiver. In this use,as a converter, the device which has been described is operated with theinput circuit tuned to respond to the input frequencies and the outputcircuit tuned to the desired sum or difference output frequency. As anexample of use as a converter, Fig. 8 shows a schematic diagram of theconnections for the different frequencies applied to the deviceillustrated in Fig. 1 and also shows elimination of the feedbackconnection 22, 23. Fig. 8 is a modified drawing of the portion of Fig 1included within the dashed line A. It should be understood that therepresentation of Fig. 1 in Fig. 8 might equally well be therepresentation of any of the other figures since the distinctivefeatures of Fig. 8 are the use of different frequencies and thecorresponding differently tuned input and output circuits. In suchcases, an over-all feedback connection cannot be used directly since theinput and output frequencies differ.

Fig. 8 illustrates, therefore, the changes in Fig. 1 to adapt it tofrequency conversion. The input is from two sources, l H representingthe input at one frequency f1 which may be an incoming high frequencysignal from an external source, and I22 representing the input atanother frequency f2 which may be from any other source such as a localhigh frequency oscillator. The output into load I23, which may be of anysuitable type, resistive, reactive, or a tuned circuit, may be any sumor difference frequency of f1 and )z to which the ouptput resonantcircuit in the device is tuned. Thus the output frequency may be eitherj1+fz, f1-f2 or f2f1. In practice, it would usually be one of the lattertwo difference frequencies rather than the first-mentioned sumfrequency.

The two input frequencies are applied simultaneously to the input of thedevice and therefore the input resonant circuit must be tuned to respondto both frequencies, f1 and f2 and consequently be capable of supportingelectric fields corresponding to those two frequencies. For the purposeof minimizing input loading a number of adjustments of input electrontransit time are possible. When the input frequencies are relativelyclose together, the input transit time may be made so that it issubstantially the same number of cycles for both, that is, approximately1 /4 or 2%; or 3 /4, etc., cycles for both frequencies. If thefrequencies are quite different the input transit time may be made sothat it is approximately 1 /4 or 2% or 3%, etc., cycles for one of thefrequencies and at the same time approximately a different number ofcycles, either 2 /4 or 3 /4, etc., cycles for the other frequency. Thus,the input loading may be minimized for both frequencies. When one of thetwo frequencies, as I: for example, is supplied by a source such as alocal oscillator whose power output is ample enough to makeconsiderations of losses unimportant, then there would be no need toadjust the input transit time to minimize loading on the frequency f2.The only adjustment necessary would then be one to insure that theloading for the signal frequency i1, is minimized; that is, to insurethat the input transit time is approxi- -mately 1%, 2%, etc., cycles forthe frequency ii.

In the case of a multistage device such as that of Fig. 6, any stage maybe made the one in which frequency conversion takes place with precedinor following stages acting as amplifiers of the input and outputfrequencies, respectively. In such an arrangement the input amplifierstages and the input circuit of the converter stage would be tuned tothe input frequencies and the input electron transit time would beadjusted in one of the ways indicated above, while the output circuit ofthe converter stage and the circuits of the following amplifier stageswould be tuned to the output frequency, and the input electron transittime in the output amplifier stages would be adjusted to approximately1% or 2% or 3%, etc., cycles of the output frequency to minimize theinput loading in those stages.

In a converter embodiment such as has just been described, it is evidentthat the tuning of the output and input systems to different frequenciesallows a somewhat less elaborate mechanical structure to be used forshielding the output from the input, while maintaining the same highdegree of electrical shielding. Thus in use as a con verter, the'singlegrid of Fig. 7 may be made less elaborate than when the same tube is tobe employed as an amplifier, and in fact, the grid may then approximatethe form of any one of the grids described in connection with Fig. 1.

In regard to ground connections, none of which has been indicated in thefigures, any part of the external circuit may be connected to earth toform a direct current ground for the application of biasing voltages. Asfar as the high frequency is concerned each cavity resonator is asubstantially complete system in itself and the potential of a point inone of them cannot be uniquely referred to the potential of a pointlocated in another. This property of cavity resonators is wellappreciated by those'who have worked with them and with high frequencyfield analysis treated by the usual retarded potential solution ofMaxwells field equations.

The illustrative embodiments presented have pictured desirable physicalstructures which avoid long high frequency leads and inefficient circuitelements and provide the shielding and the types of circuits which makepossible the operating conditions under which benefits of the essentialelectron transit time adjustments may be had. First, the input transittime must lie within the range where input loading is compensated for bythe negative resistance of the electron stream as has been defined.Second, the output transit time must be short so that the gain of thesystem is maintained at high frequencies. Third, the input and outputresonant systems must be constructed so as to couple directly to theelectron stream, must have low high-frequency losses, and must bethoroughly shielded from each other to prevent unwanted stray couplingsfrom being present. The interdependence of these factors has notheretofore been appreciated and the studied combinations disclosedherein make possible types of performance not heretofore obtainable.

The invention may be exemplified in forms other than the typical onesshown and it is not intended that the invention be construed as limitedto these but only as defined by the appended claims.

What is claimed is:

l. A high frequency device comprising an electron discharge tubecontaining an electron emitting cathode and an anode, electricalpotential means for causing a stream of electrons to flow over a pathfrom the cathode to the anode, a.

17 high frequency input circuit comprising a substantially closedelectrical resonant system enclosthrough both systems in Series withoutprevent-.

ing thorough shielding of the input and output high frequency energies,the electrical potential means and electron path lengths through thehigh frequency fields in the input and output closed systems being suchthat the electron transit time through the input high frequency fieldlies between the period of any whole number of cycles of the highfrequency field and the period of that number increased by one-halfcycle and the electron transit time through the output high frequencyfield is less than the period of one cycle of the field.

2. A high frequency device comprising an electron discharge tubecontaining an electron emitting cathode and an anode, electricalpotential means for causing a stream of electrons to flow over a pathfrom the cathode to the anode, a high frequency input circuit comprisinga' substantially closed electrical resonant system enclosing a highfrequency electric field, a high frequency output circuit comprising asubstantially closed electrical resonant system enclosing a highfrequency electric field, the resonant systems being aligned withopenings intercepting the electron path to allow the said electronstream to pass through both systems in series without preventingthorough shielding of the input and output high frequency energies, theelectrical potential means and the electron path length through the highfrequency field in the input closed system being such that the electrontransit time through the input high frequency field is approximately theperiod of any whole number of cycles of the high frequency field andthat number increased by one-fourth cycle.

3. A high frequency device comprising an electron discharge tubecontaining an electron emitting cathode, an anode and a space chargecontrol electrode, electrical potential means for causing a stream ofelectrons to flow over a path from the cathode to the anode, a highfrequency input circuit, comprising a substantially closed electricalresonant system enclosing a high frequency electric field and connectedto the space charge control electrode to efi'ect space charge control ofthe electron stream, a high frequency output circuit comprising asubstantially closed electrical resonant system enclosing a highfrequency electric field, the resonant systems being aligned withopenings intercepting the electron path to allow the said electronstream to pass through both systems in series without preventingthorough shielding of the input and output high frequency energies, theelectrical potential means and electron path lengths through the highfrequency fields in the input and output closed systems being such thatthe electron transit time through the input high frequency field rangesfrom that of any whole number of cycles of the high frequency field toone-half cycle more than that number and the electron transit timethrough the output high frequency field is less than the period of onecycle of the field.

4. A high frequency device comprising an electron discharge tubecontaining an electron emiti 18 ting cathode, an anode and a spacecharge control electrode, electrical potential means for causing astream of electrons to flow over a path from the cathode to the anode, ahigh frequency input circuit comprising a substantially closedelectrical resonant system enclosing a high frequency electric field andconnected to the space charge control electrode to effect space chargecontrol of the electron stream, a high frequency output circuitcomprising a substantially closed electrical resonant system enclosing ahigh frequency electric field, the resonant systems being aligned withopenings intercepting the electron path to allow the said electronstream to pass through both systems in series without preventingthorough shielding of the input and output high frequency energies, theelectrical potential means and the electron path length through the highfrequency field in the input closed system'being such that the electrontransit time through the input high frequency field is approximately theperiod of any whole number of cycles of the high frequency field andthat number increased by one-fourth 7 cycle.

5. A high frequency device comprising an electron discharge tubecontaining an electron emitting cathode, an anode, a space chargecontrol electrode therebetween adjacent to the cathode and an outputelectrode adjacent to the anode between the anode and the space chargecontrol electrode, electrical potential means for causing a fiow ofelectrons over a path from the cathode to the anode includingthe'control electrode and the output electrode, a substantially closedelectrical resonant system attached to the cathode and the space chargecontrol electrode to include the space between the cathode and thecontrol electrode, means for energizing at high frequency the saidresonant system whereby variations are impressed upon the electronstream and a second substantially closed electrical resonant systemattached to the said output electrode and the anode to include the spacebetween the output electrode and the anode whereby high frequency energymay be generated in the said second resonant system by the passage ofelectrons between the output electrode and the anode, the said closedresonant systems being joined to their respective electrodes so as toinclude the necessary openings to permit the passage of electronsthrough the interelectrode spaces while maintaining substantially closedelectrical boundaries for the resonant frequency except forcouplingmeans for high frequency excitation and output energies, the saidelectrical potential means and the spacing of the electrodes being suchthat the electron transit time between the cathode and the space chargecontrol electrode is a period between that of any whole number of cyclesof the energizing high frequency and the period of that number increasedby one-half cycle and the electron transit time between the said outputelectrode and the anode is less than the period of one cycle of the highfrequency.

trondischarge tube containing an electron emitting cathode, an anode, a.space charge control electrode therebetween adjacent tov the cathode 6.A high frequency device comprising an elecspace charge control electrodeto include the space between the cathode and the contro1 electrode,means for energizing at high frequency the said resonant system wherebyvariations are impressed upon the electron stream, a secondsubstantially closed electrical resonant system attached to the saidoutput electrode and the anode to include the space between the outputelectrode and the anode whereby high frequency energy may be generatedin the said second resonant system by the passage of electrons betweenthe output electrode and the anode, the said closed resonant systemsbeing joined to their respective electrodes so as to include thenecessary openings to permit the passage of electrons through theinterelectrode spaces while maintaining substantially closed electricalboundaries for the'resonant frequency except for coupling means for highfrequency excitation and output energies, and a feedback circuitconnecting the two closed resonant systems whereby high frequency energymay be introduced into the first-mentioned system from thesecond-mentioned system, the said electrical potential means and thespacing of the electrodes being such that the electron transit timebetween the cathode and the space charge control electrode is a periodbetween that of any whole number of cycles of the energizing highfrequency and the period of that number increased by one-half cycle andthe electron transit time between the said output electrode and theanode is less than the period of one cycle of the high frequency.

7. A high frequency device according to claim 6 in which theenergization of the first-mentioned resonant system is entirely by meansof the feedback connection from the second-mentioned resonant system.

8. A high frequency device according to claim 6 in which the feedbackconnection is such that the energy introduced by it into thefirst-mentioned resonant system is in opposite phase to the energyintroduced into that system by the first-mentioned energizin means,whereby the gain is stabilized and the distortion reduced.

9. A high frequency device comprising a plurality of electron dischargetubes operatin in tandem, each tube containing an electron emittingcathode, an anode, a space charge control electrode therebetweenadjacent to the cathode and an output electrode adjacent to the anodebetween the anode and the space charge control electrode, electricalpotential means for causing electrons to flow from the cathodes to theanodes over paths including the respective control and outputelectrodes, each tube having a substantially closed electrical resonantsystem attached to the cathode and space charge control electrode toinclude the space between the cathode and the space charge controlelectrode and a substantially closed electrical resonant system attachedto the said output electrode and the anode to include the space betweenthe output electrode and the anode, the said closed resonant systemsbeing joined to their respective electrodes so as to in-' clude thenecessary openings to permit the passage of electrons through theinterelectrode spaces while maintaining substantially closed electricalboundaries for the resonant frequency except for coupling means for highfrequency excitation and output energies, means for energizing at highfrequency the resonant system attached to the space charge controlelectrode of the first of the series of tubes whereby variations areimpressed upon the electron stream, means whereby the resonant systemattached to the space charge control element of each tube following thefirst tube of the series is energized from the output energy of thepreceding tube, the electrical potential means and the electron pathlengths between the electrodes of the tubes being such that the electrontransit time between each cathode and the'adjacent space charge controlelement is a period between that of any whole number of cycles of theenergizing high frequency and the period of that number increased byone-half cycle.

10. A high frequency device comprising a plurality of electron dischargetubes operating in tandem, each tube containing an electron emittingcathode, an anode, a space charge control electrode therebetweenadjacent to the cathode and an output electrode adjacent to the anodebetween the anode and the space charge control electrode, electricalpotential means for causing electrons to flow from the cathodes to theanodes over paths including the respective control and outputelectrodes, each tube having a substantially closed electrical resonantsystem attached to the cathode and space charge control electrode toinclude the space between the cathode and the space charge controlelectrode and a substantially closed electrical resonant system attachedto the said output electrode and the anode to include the space betweenthe output electrode and the anode, the said closed resonant systemsbeing joined to their respective electrodes so as to include thenecessary openings to permit the passage of electrons through theinterelectrode spaces while maintaining substantially closed electricalboundaries for the resonant frequency except for coupling means forhigh' frequency excitation and output energies, means for energizing athigh frequency the resonant system attached to the space charge controlelectrode of the first of the series of tubes whereby variations areimpressed upon the electron stream, means whereby the resonant systemattached to the space charge control element of each tube following thefirst tube of the series is energized from the output energy of thepreceding tube, and a feedback circuit connecting one of the closedresonant systems attached to an output electrode with a preceding closedresonant system attached to a space charge control element, theelectrical potential means and the electron path lengths between theelectrodes of the tubes being such that the electron transit timebetween each cathode and the adjacent space charge control element is aperiod between that of any whole number of cycles of the energizing highfrequency and the period of that number increased by one-half cycle.

11. A high frequency device comprising a plurality of electron dischargetubes operating in tandem, each tube containing an electron emittingcathode, an anode, a space charge control electrode therebetweenadjacent to the cathode and an output electrode adjacent to the anodebetween the anode and the space charge control electrode, electricalpotential means for causing electrons to flow from the cathodes to theanodes over paths including the respective control and outputelectrodes, each tube having a substantially closed electrical resonantsystem attached means whereby the resonant system attached to the spacecharge control element of each tube following the first tube of theseries is energized from the output energy of the preceding tube, and afeedback circuit connecting one of the closed resonant systems attachedto an output electrode with a preceding closed resonant system attachedto a space charge control element, the electrical potential means andthe electron path lengths between the electrodes of the tubes being suchthat the electron transit time between each cathode and the adjacentspace charge control element is a period between that of any wholenumber of cycles of the energizing high frequency and the period of thatnumber in-' creased by one-half cycle, and the electron transit timebetween each anode and the adjacent output electrode is less than theperiod of one cycle of the high frequency.

12. A high frequency device comprising an electron discharge tubecontaining an electron emitting cathode and an anode, electricalpotential means for causing a stream of electrons to flow over a pathfrom the cathode to the anode, a high frequency input circuit comprisinga, substantially closed electrical resonant system enclosing a highfrequency electric field, a high frequency output circuit comprising a.substantially closed electrical resonant system enclosing a highfrequency electric field, the resonant systems being aligned withopenings intercepting-the electron path to allow the said electronstream to pass through both systems in series without preventingthorough shielding of the input and output high frequency energies, andmeans for producing a virtual cathode at a point along the electron pathclose to where the electrons enter the high frequency input system, theelectrical potential means and electron path lengthsthrough the highfrequency fields in the input and output closed systems being such thatthe electron transit time through the input high frequency field is aperiod between that of any whole number of cycles of the high frequencyfield and the period of that number increased by one-half cycle and theelectron transit time through the output high frequency field is lessthan the period of one cycle of the field.

13. A high frequency device comprising an electron discharge tubecontaining an electron emitting cathode and an anode, electricalpotential means for causing a stream of electrons to flow over a pathfrom the cathode to the anode, a high frequency input circuit comprisinga substantially closed electrical resonant system enclosing a highfrequency electric field, a high frequency output circuit comprising asubstantially closed electrical resonant system enclosing a, highfrequency electric'field, the resonant system being aligned withopenings intercepting the electron path to allow the said electronstream to pass through both systems in series without preventingthorough shielding of the input and output high frequency energies, anda feedback circuit connecting the two closed resonant systems wherebyhigh frequency energy may be intro duced into the first-mentioned systemfrom the second-mentioned system, the electrical potential means and theelectron path lengths through the high frequency fields in the input andoutput closed systems being such that the electron transit time throughthe input high frequency field is a period between that of any wholenumber of cycles of the high frequency field and the period of thatnumber increased by one-half cycle and the electron transit time throughthe output high frequency field is less than the period of one cycle ofthe field. t

14. A high frequency device comprising an electron discharge tubecontaining an electron emitting cathode and an anode, electricalpotential means for causing a stream of electrons to flow over a pathfrom the cathod to th anode, a high frequency input circuit comprising asubstantially closed electrical resonant system enclosing a highfrequency electric field, a high frequency output-circuit comprising asubstantially closed electrical resonant system enclosing a highfrequency electric field, the resonant systems being aligned withopenings intercepting the electron path to allow the said electronstream to pass through both systems in series without preventingthorough shielding of the input and output high frequency energies, anda controlelectrode in the path of the electron stream between thecathode and the entrance to the resonant system comprising the inputcircuit, the electrical potential means and the electron path lengththrough the high frequency field in the input closed system being suchthat the electron transit time through the input high frequency field isa period between that of any whole num ber of cycles of the highfrequency field and the period of that number increased by one-halfcycle.

15. A high frequency device comprising an electron discharge tubecontaining an electron emitting cathode, an anode and a space chargecontrol element therebetween, electrical potential means for causing astream of electrons to fiow from the cathode to the anode through thespace charge control element, a high frequency input circuit comprisinga substantially closed electrical resonant system enclosing a. highfrequency electric field and including space traversed by the electronstream between the cathode and the space charge control element, a highfrequency output circuit comprising a substantially closed electricalresonantsystem enclosing a high frequency electric field and includingspace traversed by the electron stream between the space charge controlelement and the anode, the electrical potential means and the electronpath lengths being such that the electron transit time through the highfrequency field in the input closed system lies between the period ofany whole number of cycles of the high frequency field and the period ofthat number increased by one-half cycle.

16. A device according to claim 2 characterized in that the twoelectrical resonant systems are resonant at the same frequency.

17. A device according to claim 2 characterized in that the twoelectrical resonant systems are resonant at different frequencies.

18. A device according to claim 11 characterized in that the severalelectrical resonant systems are resonant at the same frequency.

19. A device according to claim 11 characterized in that the severalelectrical resonant systerns are resonant at frequencies not one and thesame.

20. A' [high frequency device comprising an electron discharge tubecontaining an electron emitting cathode and an anode with a surfacecoating adapted to emit secondary electrons, electrical potential meansfor causing a streamof electrons to flow over a path from the cathode tothe anode, a high frequency input circuit com- I prising a substantiallyclosed electrical resonant system enclosing a high frequency electricfield, a high frequency output circuit comprising a substantially closedelectrical resonant system enclosing a high frequency electric field,the resonant systems being aligned with openings intercepting theelectron path to allow the said electron stream to pass through bothsystems in series without preventing thorough shielding of the input andoutput high frequency energies, the electrical potential means and theelectron path length through the high frequency field in the inputclosed system being such that the electron transit time through theinput high frequency field is approximately the period of any wholenumber of cycles of the high frequency field and that number increasedby one-fourth cycle.

21. A high frequency devicecomprising an electron discharge tubecontaining an electron emitting cathode and an anode, electricalpotential means for causing a stream of electrons to flow over a pathfrom the cathode to the anode, a high frequency input circuit comprisinga substantially closed electrical resonant system enclosing at least twohigh frequency electric fields of different frequencies, a highfrequency output circuit comprising a substantially closed electricalresonant system enclosing a, high frequency electric field, the resonantsystems being aligned 24 with opening intercepting the electron path toallow the said electron stream to pass through both systems in serieswithout preventing thorough shielding of the input and'output highfrequency energies, the electrical potential means and the electron pathlength through the high frequency fields in the input closed systembeing such that the electron transit time through the input highfrequency fields is approximately the period of any whole number ofcycle of the fields and that number increased by one-fourth cycle.

22. A device according to claim 21 characterized in that the electrontransit time through the input high frequency fields is approximatelythe period of the same whole number of cycles of each field and thatnumber increased by onefourth cycle.

23. A device according to claim 21 characterized in that the electrontransit time through the input high frequency fields is approximatelythe period of a different whole number of cycles of the different fieldsand those numbers increased by one-fourth cycle.

24. A device according to claim 21 characterized in that the electrontransit time through the input high frequency fields is approximatelythe period of any whole number of cycles of at least one of the fieldand that number increased by one-fourth cycle.

FREDERICK B. LLEWELLYN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,106,771 Southworth Feb. 1, 19382,190,668 Llewellyn Feb. 20, 1940

